Molecular recognition by cesium tetrabenzo-24-crown-8

Two crystal structures of cesium tetrabenzo-24-crown-8 complexes are report ed. Solvent molecules 4-methylmorpholine (1) and ethylene glycol (2) are ob served to coordinate cesium within two clefts created by the cation-crown e ther complex. Careful examination of the structures suggests that while bot h complexes exhibit sterically crowded clefts, the binding of cesium to the crown ether is perturbed only in 2. C-H . . . pi hydrogen bonding is obser ved between the clefts and the included guests. The ethylene glycol complex 2 forms a complex O-H . . .O hydrogen bond network between free and bound glycol and nitrate.